1. Field of the Invention
The present invention relates to a trailer hitch arrangement for attachment to the drawbar of a towing vehicle and which is suitable for lifting and aligning a trailer tongue in place on a towing ball member mounted on the drawbar.
2. Prior Art
Aligning a trailer tongue with a conventional drawbar, provided with the usual ball member, is often difficult, since the ball member cannot be seen by the driver of the vehicle. Also, with a heavy trailer it may be difficult to lift the trailer tongue to just the right height required to engage the ball member. Various self-aligning and self-connecting hitch arrangements have been proposed to overcome these problems, for example those described in the following U.S. patents:
No. 4,657,275, issued Apr. 14, 1987 to Carroll;
No. 4,903,978, issued Feb. 27, 1990 to Schrum, 111;
No. 5,080,386, issued Jan. 14, 1992 to Lazar;
No. 5,435,587, issued Jul. 25, 1995 to Beddows; and
No. 5,503,422, issued Apr. 2, 1996 to Austin.
All of these patents show mechanisms in which, as the towing vehicle is backed into place, the trailer tongue is lifted to a suitable height to engage the towing ball member by a ramp mounted to the rear of the ball member, while the tongue is guided laterally by flanges or sidewalls which diverge outwardly and rearwardly from near the sides of the ball member. In the Austin patent, the ramp is removed manually when the tongue has reached the desired position over the ball member, and the tongue is then lowered onto the ball member. In the other patents, the ramp is arranged to drop automatically when the tongue has reached a suitable position over the ball member, so as to allow the tongue to fall into place on the ball member.
None of the arrangements shown in these prior patents appears to be in widespread use. It is believed that this may be due to the prior designs having one or more of the following drawbacks:
a) Undue complexity and expense; PA1 b) Awkwardness in use, particularly in requiring dismantling or removal and storage of several parts; and PA1 c) Imposing restrictions on the movement of the tongue.
As indicated, in the Austin patent there is no automatic release or drop of the ramp member, so a series of manual operations are required to remove this and to lower the tongue. The Beddows patent shows a design in which, as the tongue moves into position, the ramp member firstly falls by a short distance, allowing partial engagement of the tongue with the ball member. To complete the connection, the ramp is allowed to drop further, and is then removed and stored separately. This arrangement is complex.
In the other three patents the ramp is hinged behind the ball member, i.e. on the trailer side of the ball member, and drops from an upwardly inclined position to a roughly horizontal position as the tongue moves into position, allowing the tongue to engage the ball member.
In the Lazar patent, the ramp member, having fallen to the horizontal position, remains in this position; this would seem to limit the downward pivoting of the tongue, which would interfere with the ramp member if it were to swing down more than about 10.degree. from the horizontal. Normally, a trailer hitch should allow 20.degree. or more downward pivoting of the tongue relative to the drawbar, from the normal horizontal position. In the Carroll design, parts including the ramp member, the extension which holds the ramp member, and the support which temporarily holds the ramp member, have to be separately removed, which is somewhat awkward. If they were not removed, they would certainly interfere with movement of the tongue. In the Schrum design, the ramp remains in place; this is possible since the ramp pivot is low relative to the ball member. However, this results in a steep ramp angle, of about 55.degree. to the horizontal, and appears to require special anti-friction elements on the trailer tongue; presumably it would not work properly with a conventional tongue. The steep angle seems to result from a need to keep the pivot clear of the tongue, while at the same time avoiding having a large fixed extension behind the ball member.
These drawbacks of the last three patents are related to the placement of the ramp hinge behind (i.e. on the trailer side of) the ball member. Either this hinge will interfere with required movement of the tongue, as in Lazar, or it will require that the ramp and associated parts be removed, as in Carroll, or it will need a very steep ramp, as in Schrum.